With support from the US Smart Grid Demonstration Program, Texas utility Oncor has demonstrated that the increased grid capacity available from dynamic line rating (DLR) technologies can be practically and automatically applied on a commercial basis.
Demonstrating increased reliability, reduced cost of electricity, and improved access to renewable energy, the results also confirm the high potential of DLR systems.
Implementation of dynamic line rating
The primary objective of the nearly US$7.3 million project was to demonstrate the repeatable, practical implementation of DLR technologies from transmission line sensors to wholesale electric markets.
Oncor deployed DLR on eight transmission lines in central Texas used in the daily operations and wholesale electricity market of both the company itself and the independent system operator, the Electric Reliability Council of Texas (ERCOT). The primary technology deployed was Nexans’ CAT-1 System, which is composed of load cells to measure conductor tension and sensors to measure net radiation temperature. In addition for validation and verification tasks Oncor deployed EDM International’s Video Sagometer system, which measures conductor sag, and Promethean Devices’ Real-Time Transmission Line Monitoring System (RT-TLMS), which measures conductor clearance.
DLR improves grid efficiency and reliability
The project demonstrated that dynamic ratings are a valuable and successful tool to increase the real-time capacity of a transmission line, enabling transmission owners and system operators to mitigate congestion, increase system reliability, and follow a “least-regrets” strategy for capital spending.
Oncor determined that, for most transmission lines, the dynamic rating typically delivers an increased real-time capacity above the ambient-adjusted rating 80%-95% of the time and above the static rating 97%-99% of the time. While quarterly results varied, the real-time capacity delivered by dynamic ratings was 6%-14% greater than ambient-adjusted rating for 345kV lines and 8%-12% greater than ambient-adjusted rating for 138kV lines. This additional capacity was available 84%-91% of the time.
It was not possible to quantify the real-time, congestion-related benefits of deploying DLR technologies, but based on modelling Oncor determined that 5% additional capacity would likely relieve congestion by up to 60% on the target lines with DLR installed, while 10% additional capacity would practically eliminate all congestion on the target lines. Based on 2012 congestion levels and costs, Oncor extrapolated that the total congestion impact savings potential resulting from an ERCOT-wide DLR deployment would amount to approximately $20 million, a 3% reduction.
Oncor also calculated the savings associated with the deferral of other transmission upgrades, finding that installing DLR systems is often only a fraction of the cost of other solutions (although the rating increase is less than with other transmission upgrades).
Lessons for DLR deployment
Oncor’s deployment aimed to overcome the main barriers to DLR deployment, which has typically taken place for transmission system planning purposes or research and development (R&D) tasks.
Key lessons learned are:
- The need to monitor the entire transmission line rather than a few “critical spans”
- The benefits of a “total-system” approach to DLR integration, which considers the next limiting element on the grid and the role of the DLR system in the greater context of grid operations (i.e., maintains a safe operating range of the relay protection settings on the line)
- The reality that, while a DLR system can increase ratings by as much as twofold on a line, the “usable” range of increased capacity is between a 5% and 30% above the static rating, depending on the probability that the increased capacity is available
- The superiority of utilizing dynamic ratings in real-time operations, which fully captures the technology’s benefits in terms of increased wide-area situational awareness and improved grid reliability and flexibility, rather than in planning studies, which focus on the probability that a rating is available a certain percentage of the time
Further DLR deployments
Since this project was undertaken Oncor has continued to invest in additional DLR systems to address capacity needs elsewhere in its service territory. A second project, the West Texas DLR Project, was initiated in January 2013 to relieve congestion around Odessa, Texas. DLR installation was implemented on five lines rated 69kV and 138kV, and became operational in June 2013, including full, real-time integration with ERCOT’s economic dispatch tool.
Additional lines for DLR deployment are under assessment, based on planning needs and congestion exposure.